1. Technical Field
The invention relates to a pixel structure. Particularly, the invention relates to an in-plane switching pixel structure.
2. Related Art
In a vertical alignment in-plane switching (VA-IPS) display panel, a VA-type liquid crystal is used in collaboration with IPS-type pixel electrodes to achieve both of the characteristics, where the pixel electrode generally has a plurality of branches and a plurality of alignment slits located between the branches. In the VA-IPS display panel, when a voltage is not applied, the liquid crystal molecules are vertically aligned, so that light cannot penetrate there through. When the voltage is applied, an electric field at two edges of each branch of the pixel electrode is stronger, and the liquid crystal molecules at such place tilt at first. However, the electric field at the slit center between the branches of the pixel electrodes is weaker. The liquid crystal molecules at the slit center of the pixel electrodes tilt along the both edges of the branches of the pixel electrodes and conflict to each other, so that the liquid crystal molecules at certain regions are still vertically aligned. Therefore, a disclination line is formed between the branches of the pixel electrode.
Generally, when the applied voltage is switched from a larger voltage to a smaller voltage, if the vertically-aligned liquid crystal molecules exist in the middle of the slit, the liquid crystal molecules at two edges of the slit are pulled by elasticity of liquid crystal to return to a correct tilting direction. However, if the liquid crystal molecules between the branches of the pixel electrode all lie down rather than vertically-aligned, the lying-down liquid crystal molecules in the middle of the slit are simultaneously pulled by elasticity from both edges in opposite directions, so that the lying-down liquid crystal molecules are not easy to return back to a vertically-aligned state. In this way, the disclination line can be abnormal or disappeared, which may result in a phenomenon of image retention of the display panel.
In the commonly used VA-IPS display panel, one pixel structure generally includes two pixel electrodes, and an opening is formed at a junction of the two intersected pixel electrodes. An external electric field probably influence the tilting direction of the internal liquid crystal molecules through the opening. In this way, the originally vertically-aligned liquid crystal molecules located between the pixel electrodes are probably interfered by the external electric field to lie down. Moreover, the lying-down liquid crystal molecules may influence a tilting direction of the other liquid crystal molecules along the disclination line, and result in a fact that the vertically-aligned liquid crystal molecules between the branches of the pixel electrodes sequentially lie down. Namely, the external electric field probably causes abnormity or disappearance of the disclination line, and the liquid crystal display panel has a defect of image retention.